1. Field of the Invention
The present invention relates to a vibration isolating apparatus which, for example, is used to prevent transmission of vibration from a vibration generating portion, and particularly to a vibration isolating apparatus which is applicable to, for example, an engine mount for preventing transmission of engine vibration to a vehicle body, other vehicles, a general industrial machine or the like.
2. Description of the Related Art
Heretofore, a vibration isolating apparatus used as an engine mount is disposed between an engine which is a vibration generating portion of a vehicle and a vehicle body which is a vibration receiving portion. In such a vehicle, the vibration isolating apparatus absorbs vibration generated by the engine and prevents the vibration from being transmitted to the vehicle body.
As an example of this type of vibration isolating apparatus, there has been known a vibration isolating apparatus 110 as shown in FIG. 4. The vibration isolating apparatus 110 is described below with reference to FIG. 4.
The vibration isolating apparatus 110 is constructed as follows. A rubber elastic body 116 is disposed between a top plate 112 and a bottom plate 114. Further, a liquid chamber 118 filled with liquid is provided inside of the elastic body 116 and is divided into a pair of liquid chambers 118A, 118B by a rubber membrane 120, and an orifice 122 causes these liquid chambers 118A, 118B to communicate with each other. When the engine mounted on the vibration isolating apparatus 110 operates and vibration is generated, vibration is absorbed by damping force which is generated by a damping function of the elastic body 116, deformation of the membrane 120, viscous resistance of a liquid within the orifice 122 provided for communication between the liquid chambers 118A, 118B, or the like. As a result, transmission of vibration is prevented.
However, in the above-described vibration isolating apparatus 110, although vibration in a low frequency range is damped by the orifice 122, the membrane 120, or the like, when vibration is a higher frequency range is transmitted to the vibration isolating apparatus 110, the orifice 122 becomes clogged or the membrane 120 may not sufficiently deform. For this reason, an internal pressure within the liquid chamber 118A increases and a spring constant increases. As a result, there is a drawback in that vibration cannot be sufficiently reduced.